International Journal of Hydrogen Energy 26 (2001) 935–940www.elsevier.com/locate/ijhydene

Pre-reforming of lique)ed petroleum gas onsupported ruthenium catalyst

Takashi Suzuki ∗, Hiko-ichi Iwanami, Osamu Iwamoto, Tamio KitaharaResearch and Development Center, Cosmo Research Institute (CRI), 1134-2, Gongendo, Satte, Saitama 340-0193, Japan

Abstract

Cylindrical shaped CeO2–Al2O3 support was prepared by calcining the pelletized powder mixture of cerium carbonate,aluminum hydroxide and poly-vinylalcohol. The speci)c surface area and porosity of the support were improved relative tothose obtained by a conventional method. Ru was loaded on the porous carrier by using ruthenium trichloride and aqueousammonia. The dispersion of Ru was improved 2.2 fold as much as that in the case using a conventional catalyst. The improvedcatalyst showed high activity for pre-reforming of lique)ed petroleum gas (LPG) with low proportion of S=C as 0.8 at450

◦C. Finally, 7000 h of sustained run of the pre-reforming was successfully achieved on that catalyst. ? 2001 International

Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.

1. Introduction

Recently, production of deeply desulfurized fuels, fuelcell systems, gas to liquid (GTL) process, and others wereconsidered to be important technologies developed to obtainclean energy sources. Rationalized reforming would be thekey technology in the above mentioned categories. More-over, it might be considered that the demand of hydrogenwill be further increased in the near future.

A steam reforming of hydrocarbons is one of the leastexpensive hydrogen production methods at the present time[1]. It is considered that the way to improve the energy e?-ciency in the steam reforming process would be important.Some researchers have pointed out that low temperature re-forming, namely, the pre-reforming is one of the e@ectivetechniques to enhance the thermal e?ciency [2–4] and thatthe fuel saving in the process could be increased by 9.2%relative to the process without the pre-reformer [4].

The major role of the pre-reformer is to convert lighterhydrocarbons such as LPG into methane. In order to obtainmethane preferentially, the pre-reforming of LPG should

∗ Corresponding author. Tel.: +81-480-42-2211; fax: +81-480-42-3790.

E-mail address: takashi suzuki@cosmo-oil.co.jp (T. Suzuki).

be carried out at lower temperatures such as 400–500◦C

from the equilibrium viewpoints. In addition, the carbon de-position caused by Boudouard reaction (2CO → CO2 +C ↓) [5] dominantly occurs in the range of lower tem-peratures. Therefore, a catalyst having higher activity andhigher resistance to the carbon deposition is desired for thepre-reforming facility.

It is suggested that ruthenium-based catalyst is very ef-fective in preventing carbon deposition during the steamreforming, that the catalyst system is readily poisoned bysulfur compounds and that the carbon deposition takes placeon the poisoned ruthenium based catalyst [6–8]. Alkali metalis doped in reforming catalyst as a means of resisting car-bon formation [9]. Recently, it has been reported on theRu=Al2O3 for high temperature steam reforming that ceriumoxide has a role to prevent poisoning by sulfur and as a re-sult carbon deposition can be reduced [10].

However, the cerium oxide doped Ru=Al2O3 for hightemperature reforming does not show su?cient activitiesfor the pre-reforming. In order to improve the catalyst ac-tivity for the pre-reforming, an increase in the number ofactive sites by improving dispersion would be e@ective. Inthis work, when decomposable organic compounds such aspoly-vinylalcohol were added to the starting material of asupport, the surface area and porosity were improved, and asa result, the dispersion of ruthenium was increased 2.2 fold

0360-3199/01/$ 20.00 ? 2001 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.PII: S0360 -3199(01)00036 -2

936 T. Suzuki et al. / International Journal of Hydrogen Energy 26 (2001) 935–940

in comparison with the support prepared by the conventionalmethod. Finally, the catalyst was subjected to preliminarysustained run of the pre-reforming; the catalyst performancewas maintained for 7000 h.

2. Experimental

2.1. Porous CeO2–Al2O3 support

Powder mixture of Ce2(CO3)3 · 8H2O (Kanto ChemicalCo.), Al(OH)3 (Kanto Chemical Co.) and poly-vinylalcohol(PVA; Nihon Gosei Co.) was well ground and sieved under100 mesh. PVA was added to contain 10 wt% to the startingmaterial. The powder mixture was pressed by a pelletizer(FK-1, Systems Engineering Co.) with 16 tons=cm2. Finally,the resulting material was calcined overnight in an electricoven maintained at 650

◦C to obtain CeO2–Al2O3 support.

Then ca. 3 mm � o.d.×ca. 3 mm (H) of pellet comprisingCeO2 (7.6 wt%) and Al2O3 (92.4 wt%) was obtained. Thespeci)c surface area of the cylindrical support was around250 m2=g.

2.2. Conventional CeO2–Al2O3 support

Powder mixture of CeO2, and �-Al2O3 was used for prepa-ration. The handling procedure is the same as in Section 2.1.except for adding PVA. The speci)c surface area of thecarrier was around 140 m2=g. The porous support and con-ventional support are denoted as support-A and -B, respec-tively. The chemical composition of support-B was almostanalogous to that of support-A.

Scheme. 1. Diagram of the apparatus used for pre-reforming. PR: pressure regulating valve, FR: Kow regulating valve, PM: pressuremaintaining valve, S: gas–liquid separator, GF: gas Kow meter, and SV: stop valve.

2.3. Ru loading

Ru was loaded by means of an impregnating technique.The support was immersed into water soluble RuCl3 · H2O(Mitsuwa Chemical Co.) for 3 h at room temperature and itwas dried in air at 105

◦C for several hours. The resulting

material was soaked in 7 M of aqueous ammonia for 2 h at30

◦C. The solution was colored slightly rose pink whichmay

be caused by the formation of ammonium complexes of Ru.The specimen was rinsed with de-ionized water to removeexcess ammonia and ammonium chloride. It is deduced thatthe ruthenium chloride on the support would be changed intoruthenium hydroxide during the treatment in the alkalinesolutions.

2.4. Pre-reforming reaction

Pre-reforming reaction was performed in the conven-tional )xed bed reactor described in Scheme 1. Ten milliliter(ca. 9.5 g) of the catalyst was set in the )xed bed reactorand the catalyst was reduced by hydrogen for 3 h at 450

◦C

prior to the pre-reforming. The commercially availableLPG purchased from Cosmo Oil Co. (C4H10 : 96 vol%,C3H8 : 4 vol%) was used without further puri)cation. Molarproportions of steam=carbon in LPG (S=C) and GHSV (gashourly space velocity) were 0.8 and ca. 1500 vol /vol=h1

at 450◦C, respectively. The product distributions were

determined with TCD-GC and FID-GC (GC390, GL Sci-ence Co. Ltd.). Active carbon (Unibeads-A, 60–80 mesh,GL Science Co. Ltd.) was used for the separation ofH2, CO, CO2, and CH4, and Porapak-QS (60–80 mesh,Waters Co. Ltd.) was used for the separation of hydro-carbons.

T. Suzuki et al. / International Journal of Hydrogen Energy 26 (2001) 935–940 937

Scheme. 2. Flow diagram of CO adsorption instrument. SV: stopvalve, PG: pressure gauge, PS: pressure sensor, 6DV: 6 directionsvalve, RM: rotameter, A: adsorption vessel, and TCD: thermalconductivity detector.

2.5. Catalyst characterization

Speci)c surface area and pore volume were measured bymeans of a Belsorp 28 instrument (Bel Japan Co.) using ni-trogen as an adsorbable molecule. The dispersion of Ru canbe calculated appropriately on the assumption that CO isadsorbed dominantly with a stoichiometric adsorption rateof CO : Ru =1 : 1, which is reported in the Refs. [11,12].The dispersion is represented as [CO(a)]=[Ru]×100 (%),where [CO(a)] is the adsorbed amount of CO and [Ru] isthe concentration of Ru in catalyst [11]. [CO(a)] is deter-mined precisely by pulse adsorption method [13–15] andthe concentration of [Ru] is obtained by a JXA-8600MX(JEOL Co.) ICP (induced coupled plasma) instrument. Priorto the pulse adsorption, 0.5 g of specimen was set in thequartz U-tube and it was reduced at 450

◦C for 3 h. Then

the specimen was cooled from 450◦C to 25

◦C under Kow-

ing helium. After the pretreatment, CO pulse (0.2 ml) wasdosed to the catalyst. The CO pulse was repeated until theadsorption was saturated. The amount of adsorbed CO wasobtained by accumulating peak areas of TCD. The CO usedwas of 99.95% purity (research grade, Takachiho Chemi-cal Co.), and the pulse experiment was carried out by usingan Ohkura 6850 adsorption instrument equipped with TCD(Ohkura Riken Co.) . The connection diagram of the instru-ment is described in Scheme 2. The chemical compositionsof Ru, CeO2, and Al2O3 in these catalysts were 1.6, 7.5, and90.9 wt%, respectively. Distribution of ruthenium speciesin the catalyst was observed by an IRIS Advantage-RP(Jarrell-Ash Co.) EPMA (electron probe micro analysis)instrument.

3. Results and discussion

3.1. Ruthenium distributions in Support-A and -B

The speci)c surface area of Support-A is ca. 250 m2=g,whereas that of Support-B is 0.56 fold in comparison withthe case of support-A. In order to obtain further informa-tion, the pore volume on the catalysts was con)rmed. Thepore volume of Support-B was 0.42 ml=g, whereas thatof Support-A was 0.64 ml=g. These observations impliedthat the texture of the support was improved by addingPVA.

When Support-A and Support-B were used for cat-alyst preparations, dispersion of Ru on Support-A was64.8% ((CO(a)= 2:4 ml=g-cat (stp)), whereas that of Ru onSupport-B was 29.7% ((CO(a)= 1:1 ml=g-cat(stp)) and asa result, the dispersion of Ru on Support-A was increased2.2 fold in comparison with the case of Support-B.

Fig. 1 shows the EPMA results on Ru=Support-A andRu=Support-B. In the case of Ru=Support-B, rutheniumspecies preferentially existed in the external zone, while inthe case of Ru=Support-A, ruthenium species existed notonly in the external zone but also in the internal zone. Itis, therefore, considered that the dispersion of rutheniummight be improved on Support-A and that the di@usedLPG and steam in the internal zone may react, and as aresult an increase in the whole reactivity of the cylindri-cal shape of the catalyst could be expected. In addition,it was deduced that the porosity of the support might beimproved by adding PVA as an estimated model describedin Fig. 2.

In this section, it has been suggested that the additionof a decomposable component such as PVA can increasethe speci)c surface area which in turn could inKuence thedispersion of active metal as well.

3.2. Con4rmation of catalytic performance onRu=Support-A and -B

Comparing the catalytic performance of pre-reformingon Ru=Support-A and Ru=Support-B, these catalysts weresubjected to the reaction at 450

◦C with S=C=0:8 under

8 kg=cm2 and GHSV was set at 1500 vol=vol=h1. When theRu=Support-B was used for the pre-reforming, the conver-sion of LPG was calculated by using Eq. (1) and it was85.2%, whereas when using the Ru=Support-A, LPG reactedcompletely as shown in Table 1.

Conversion of LPG (%)=100× [C] in CO + CO2 + CH4=[C] in LPG: (1)

Here, one can suspect that the lower conversion observedon Ru=Support-B would be caused by carbon formation. Itis anticipated that the carbon deposition might take placereadily in the reaction conditions as stated in the beginning.In order to clarify the di@erence of the amount in the de-posited carbon on these catalysts, they were subjected to

938 T. Suzuki et al. / International Journal of Hydrogen Energy 26 (2001) 935–940

Fig. 1. The EPMA image of Ru dispersed on Support-A and -B.

Fig. 2. Estimated model to form pores during the calcining. (•) oxides, (◦) decomposable component (PVA).

carbon analysis by using carbon analyzer (Model EMIA-110,Hitachi-Horiba Co.). The amount of deposited carbon wasdetermined on the basis of the amount of carbon dioxidegenerated in a micro electric furnace with pure oxygen. Thedeposited carbon at 100 h was ca. 0.1 g per g-catalyst onRu=Support-A and -B. Thus the deposited carbon is not somuch and the signi)cant di@erence with regard to carbondeposition was not observed on those catalysts. In addition,product distributions were almost analogous in the twocatalysts (Table 1). It is inferred from these results thatthe function of active sites on Ru=Support-A and -B werethe same but the unreacted LPG in Ru=Support-B might bedue to an insu?ciency of active sites on the catalyst. Thus,

the feed was converted completely on the texture improvedcatalyst (Ru=Support-A) which may have su?cient activesites.

As stated above, the pre-reforming reaction was success-fully performed on the Ru=Support-A with lower S=C suchas 0.8 around 450

◦C. These results led us to the preliminary

sustained run to con)rm the catalyst performance.

3.3. Preliminary sustained run

In order to con)rm the pre-reforming performance ofRu=Support-A, the catalyst was subjected to the sustainedrun for 7000 h at 450

◦C under 8 kg=cm2 in the micro reactor

T. Suzuki et al. / International Journal of Hydrogen Energy 26 (2001) 935–940 939

Table 1Conversion of butane and product distributions in low temperature steam reforminga

Time (h) Catalyst S=C Conv. of butane (%) Product distributions (%)H2 CO CH4 CO2

100 Ru=Support-A 0.8 100 9.6 0.4 73.2 16.8100 Ru=Support-B 0.8 85.2 9.3 0.3 72.6 17.8

aCatalyst: 7 ml (6.5 g), GHSV : 1500 v=v=h1, Press.: 8 kg=cm2, Temp.: 450◦C.

Fig. 3. Catalyst life test of Ru=Support-A for pre-reforming. (?) conversion of LPG, (•) methane, (4) carbon dioxide, (�) hydrogen, and(5) carbon monoxide. S=C=0:8 (at initial stage S=C=1:0), GHSV=1500, reaction temperature= 450

◦C, and pressure= 8 kg=cm2.

as seen in Scheme 1. Fig. 3 shows the conversion of LPG,and the composition of products during the pre-reforming.Evaluating the composition change in the products versusthe S=C value, the S=C was set at unity in the initial stage.The compositions of H2, CO, CH4, and CO2 in that con-dition were 13.5, 0.3, 71.9, and 14.3 vol%, respectively.After 1100 h, feeding rate of steam was decreased to main-tain S=C=0:8. The compositions of H2, CO, CH4, and CO2

were 10.9, 0.3, 74.9, and 13.9 vol%, respectively. Thus,methane was formed preferentially at lower S=C proportion.Unreacted LPG was not detected at all by means of FID-GCuntil 2500 h; after this period, an in)nitesimal amount ofbutane was observed at outlet. Finally, unreacted LPG (ca.0.3 vol% of butane) was observed after the elapse of 7000 h.However, it was observed that such a small amount of LPGwas converted completely by increasing the temperaturewithin 10

◦C.

So far, the S=Cwas maintained at a higher ratio in the con-ventional Ni based catalyst from the viewpoint of prevent-ing the carbon formations. The developed catalyst shows astable performance even in lower S=C such as 0.8 for a longterm. These results indicate that the developed Ru=CeO2–Alumina catalyst may have potential for commercialapplications.

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